In semiconductor lithography (or photolithography), the fabrication of an integrated circuit (IC) requires a variety of physical and chemical processes performed on a semiconductor (for example, silicon) substrate (which is also referred to as a wafer). A photolithography exposure apparatus or scanner is a machine that applies a desired pattern onto a target portion of the substrate. The wafer is fixed to a stage so that the wafer generally extends along a plane defined by orthogonal XL and YL directions of the scanner. The wafer is irradiated by a light beam, which has a wavelength in the deep ultraviolet (DUV) range. The light beam travels along an axial direction, which corresponds with the ZL direction of the scanner. The ZL direction of the scanner is orthogonal to the lateral XL-YL plane. The light beam is passed through a beam delivery unit, filtered through a reticle (or mask), and then projected onto a prepared wafer. In this way, a chip design is patterned onto a photoresist that is then etched and cleaned, and then the process repeats.